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WASHINGTON (CNN – Sept. 10, 2014) — It’s time to go after ISIS in Iraq and Syria, President Barack Obama said Wednesday night in a nationally televised address intended to sell stepped-up military efforts to a war-weary public.

Obama said the United States would expand its airstrikes against the Sunni jihadists in Iraq to target them across the border in Syria.

“I have made it clear that we will hunt down terrorists who threaten our country, wherever they are,” he said. “That means I will not hesitate to take action against ISIL in Syria, as well as Iraq. This is a core principle of my presidency: if you threaten America, you will find no safe haven.”

The declaration responded to calls from a growing number of U.S. politicians for such a step, with increasing public support.

Obama’s speech from the White House also sought to convince allies of a firm U.S. commitment to lead an international coalition to fight the Sunni jihadists who rampaged across northern Iraq from Syria this year. They are known as ISIS, ISIL and Islamic State.

“A steady, relentless effort”

“This counterterrorism campaign will be waged through a steady, relentless effort to take out ISIL wherever they exist, using our air power and our support for partner forces on the ground,” Obama said.

The President also announced another 475 American military advisers would go to Iraq, pushing the total figure to more than 1,000.

At the same time, he made clear the strategy differed from all-out war again in Iraq less than three years after he withdrew combat forces from the country.

“It will not involve American combat troops fighting on foreign soil,” Obama said.

Noting the formation of a new Iraqi government, which his administration has demanded, Obama announced that “America will lead a broad coalition to roll back this terrorist threat.”

Objective: “degrade and ultimately destroy” ISIS

“Our objective is clear: We will degrade, and ultimately destroy, ISIL through a comprehensive and sustained counter-terrorism strategy,” he said.

Also Wednesday, Obama shifted $25 million in military aid to Iraqi forces, including Kurdish fighters in the north combating the ISIS extremists. The aid could include ammunition, small arms and vehicles, as well as military education and training, State Department spokeswoman Marie Harf said.

U.S. diplomatic efforts this week seek to solidify the coalition. Secretary of State John Kerry left Tuesday to push Sunni leaders in Jordan and Saudi Arabia to join the United States and its allies in combating ISIS, while Defense Secretary Chuck Hagel and Lisa Monaco, the homeland security adviser, also will be in the region.

Obama has been criticized by conservatives and some Democrats for what they call a timid response so far to the threat by ISIS fighters. The recent beheading of two American journalists held captive by ISIS raised public awareness of the extremists and the threat they pose.

“We can’t erase every trace of evil from the world, and small groups of killers have the capacity to do great harm. That was the case before 9/11, and that remains true today,” Obama said.

ISIS poses a threat to the Middle East, including the people of Iraq and Syria, he said, adding: “If left unchecked, these terrorists could pose a growing threat beyond that region, including the United States.”

A senior administration official told CNN chief political analyst Gloria Borger that Obama’s message was “the next phase is offense” against ISIS, and that the President sought international support before speaking publicly about his strategy.

“Until you have a coalition, it’s hard to explain how this will work,” the official said.

Congressional authority

Obama has insisted he has the authority to ratchet up airstrikes against ISIS under war power granted more than a decade ago to fight al Qaeda. ISIS formed from some al Qaeda affiliates but is separate from the central leadership of the terrorist organization behind the September 11, 2001 attacks on the United States.

This week, he asked Congress for additional authority to arm and train moderate Syrian rebels to fight the ISIS extremists.

Such authority comes under Title 10 of the U.S. code, which deals with military powers, and Congress could vote on granting it next week. Approval also would allow the United States to accept money from other countries for backing the Syrian opposition forces.

Most voices in Congress back strong U.S. action against the ISIS fighters. However, any vote on military action can be risky, especially with congressional elections less than two months off.

The fraught politics of the issue were clear on Wednesday, when House Republican leaders put off a vote on a government spending measure set for Wednesday after pressure emerged to add the Title 10 authorization to it.

Obama initially rejected arming the Syrian opposition against President Bashar al-Assad more than two years ago to avoid getting mired in another Middle East conflict. U.S. officials also feared American weapons could end up in the hands of extremists, such as al Qaeda affiliates that eventually morphed into ISIS.

As the tide has turned against Syria’s opposition, which now finds itself fighting both government forces and ISIS, the United States began its covert aid to some rebel factions.

Until now, the U.S. strategy against ISIS has included airstrikes on the extremists in Iraq to protect several hundred American military personnel there while helping the Iraqis and providing humanitarian support.

Veteran diplomat: ISIS worse than al Qaeda

Calls for a more forceful campaign against ISIS have increased in recent months.

Former U.S. ambassador Ryan Crocker, who served in Syria, Iraq, Afghanistan, and Pakistan, told CNN on Wednesday that ISIS presents a bigger threat to America than al Qaeda.

“They are more numerous, they are better armed, they are far better financed, they are better experienced, and perhaps most critically there are several thousand of them who hold Western passports, including American passports,” Crocker said. “They don’t need to get a visa; they just need to get on a plane.”

He added: “If we don’t think we’re on their target list, we are delusional.”

After his meeting with top congressional leaders at the White House on Tuesday, Obama asked for their support to show the nation was united.He repeated that call in Wednesday’s speech.